At a news conference on Wednesday, state police chief Pete Kassetas said it appeared the victims of Tuesday's shooting — an 11-year-old boy and 13-year-old girl — were chosen randomly. The shotgun used by the suspected shooter came from his family's home and he had three rounds of ammunition, Kassetas said.

"All three rounds were expended during the incident," the police chief said. "There was no indication that he had any ammunition other than what was loaded in the gun."

The 11-year-old boy who was shot in the face and neck remains in critical condition at University Medical Center in Lubbock, Texas. The 13-year-old girl, identified as Kendal Sanders, was in satisfactory condition with injuries to her right shoulder. The family of the injured boy has asked that his name be withheld while he recovers. A school employee also suffered minor injuries.

The suspect was charged on Wednesday with three juvenile counts of aggravated battery with a deadly weapon, according to state police lieutenant Emmanuel Gutierrez. The Associated Press typically doesn't identify juveniles accused of crimes.

Meanwhile, the suspected shooter's family issued a statement saying they were heartbroken and that their remorse could not be put into words. They said the two children who were injured have been in their thoughts and prayers.

"We are horribly sad over this tragedy on so many levels," the family said. "We are praying that God will be with everyone who has been affected."

The family added it will cooperate with law enforcement to "piece together how this awful tragedy occurred".

Kassetas said investigators worked through the night executing search warrants at the school, and determined through those searches that the attack was planned. They examined the boy's locker and the duffel bag the seventh-grader used to transport the shotgun to school. Kassetas said the handle of the gun was sawed off so it had "more of a pistol grip".

He added that authorities had some indication that the boy verbally warned "select students" about the attack as he arrived at the school. Kassetas didn't elaborate.

The shooting spurred a flood of 911 calls from students on Tuesday morning. In some, screaming could be heard in the background. The shooting was over in 10 seconds, officials said, after the boy fired at the ceiling, the floor and then the students. An eighth-grade social studies teacher, John Masterson, then talked the boy into dropping his weapon.

Masterson and other teachers were lauded for taking quick action that authorities said would've saved lives had the boy had more ammunition, or had there been another gunman.

Chaves County sheriff Rob Coon said all the schools in the county, public and private, undergo regular training for dealing with "active shooters".

"The teachers and the staff at Berrendo knew exactly what to do," Coon said. "They went into their lockdown. They followed the way they were taught. If there would have been more than one young man roaming the halls, there would have been minimal damage because they locked that down so quick."

Andrea Leon, a 13-year-old eighth-grader at Berrendo, said students had completed so many drills that some started laughing when the shots first rang out "because they thought it was fake".

Police and schools nationwide adopted "active shooter" policies after two Columbine High School students, Eric Harris and Dylan Klebold, killed 12 classmates and a teacher and wounded 26 others before killing themselves in the Littleton, Colorado school's library in 1999. Police waited 45 minutes for a SWAT team to arrive before entering the school. Officers now are trained to confront a shooter immediately.

The boy in the Roswell shooting was transferred to an Albuquerque psychiatric hospital following a hearing Tuesday. His family said they were thankful the judge ordered that he receive an evaluation and mental-health treatment.